Organic compounds are those compounds which are obtained directly through natural sources like plants and animals or prepared artificially in laboratories but containing carbon and hydrogen or their derivatives. or It is a study of carbon, hydrogen and their compounds.
A homologous series is a group of organic compounds having similar structures and similar chemical properties in which the successive compounds differ by CH2 group. The various organic compounds of a homologous series are called homologues.
Example of a Homologous Series:
Homologous series of Alkanes- The general formula of the homologous series of Alkanes is CnH2n+2.
Methane – CH4
Ethane – C2H6
Propane – C3H8
Butane – C4H10
Pentane – C5H12
Homologous series of Alkenes- The general formula of the homologous series of Alkenes is CnH2n.
Homologous series of Alkynes- The general formula of the homologous series of Alkynes is CnH2n-2.
Characteristics of a Homologous Series:
Each homologous series can be represented by a general formula. For example- CnH2n+1COOH is the general formula of carboxylic acids (where ‘n‘ is the number of carbon atoms in the molecule minus 1).
The successive members of a homologous series differ by a CH2 group or by 12 + 2 x 1 = 14 mass units.
The individual members of a homologous series can be prepared by the general methods of preparation developed for that series.
The physical properties such as density, melting point, the boiling point of the members of a homologous series show a regular gradation with rising in molecular mass.
The chemical properties of the members of a homologous series are similar though the first member may vary considerably from the rest of the members.